The tunnel face excavation in rich-water mudstone stratum is liable to be unstable. The face of Badong tunnel through purple-red mudstone section collapsed, the stability of the tunnel face is evaluated as "class C stable form" based on the ADECO-RS and field investigation, and advance curtain grouting combined with pipe shed are proposed to stabilize the advanced surrounding rock. Subsequently, excavation model of the tunnel is built by means of particle flow code software to analyze the instability process of tunnel face and the deformation and failure characteristics of the surrounding rock in front. The results show that the instability process of the face presents the progressive failure characteristic of “extrusion deformation-local collapse-obvious collapse”. After the collapse, the radial direction of the arch is 4.5m, and the longitudinal direction is 15m. The loose area is developed, and the hole (crack) ratio increases from 0.1 to 0.186; the uplift area appears at the bottom of the tunnel in front of the face, and the distribution of contact force chain is Sparse, it further shows that the instability of the front of tunnel face is strong, Considering the above disturbance range of surrounding rock, advance curtain grouting parameters are proposed. Through field application, the surrounding rock reinforcement effect in front of the tunnel is good, which effectively guarantees the safety of tunnel construction, and can provide reference for the design and construction of tunnels though similar water-rich mudstone.